Small Craft Advisory 420, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKDT THU JUN 16 2011

.MODEL DISCUSSION...
MODELS OVERALL IN VERY GOOD AGREEMENT. NAM HAD BEST INITIALIZATION AND
WAS PREFERRED THROUGH THE SHORT TERM. TRENDED MID AND LONG RANGE
TOWARDS GFS/ECMWF SOLUTION. 00Z HPC DATA INCOMPLETE.

.ANALYSIS AND SHORT TERM FORECAST...

A BROAD AREA OF RAIN SHOWERS BENEATH A COLD UPPER LOW CONTINUE TO
IMPACT THE WHOLE OF SOUTHCENTRAL ALASKA THIS MORNING. WEAK SHORT WAVES
ROTATING ABOUT IN BROAD ANTICYCLONIC FLOW IN THE MID LEVELS ARE
LOCALLY ENHANCING SHOWER INTENSITY. SHOWER ACTIVITY WILL LESSEN TODAY
AS THE LOW MOVES OFF TO THE EAST...DISSIPATES OVER WESTERN CANADA LATE
FRIDAY NIGHT.

THUNDERSTORM DEVELOPMENT TODAY WILL BE LIMITED TO LOCATIONS WITH BOTH
AMPLE LOW LEVEL MOISTURE AND AVAILABLE SOLAR HEATING. THUS NORTHERN
SUSITNA VALLEY AND TALKEETNA MOUNTAINS SHOULD BE LOCUS OF CONVECTIVE
DEVELOPMENT THIS AFTERNOON AND EVENING...TOMORROW AS WELL.

MOSTLY SUNNY SKIES AND SEASONABLY WARM TEMPERATURES OVER SOUTHWEST
ALASKA TODAY THANKS TO EASTERLY OFFSHORE FLOW IN THE LOWER LEVELS AND
A RIDGE OF HIGH PRESSURE ALOFT. RIDGING TRANSLATES GRADUALLY EASTWARD
OVER NEXT 48 HOURS AND WILL INDUCE A CLEARING AND WARMING TREND OVER
SOUTHCENTRAL STARTING TOMORROW.

OUT WEST...989 MB LOW STALLED JUST SOUTH OF ATKA...BUT ASSOCIATED
OCCLUDED PROGRESSING SLOWLY EASTWARD. LOW WEAKENS TO 999 MB OVER NEXT
48 HOURS BUT REMAINS NEARLY STATIONARY. LOW THEN BEGINS TO RAPIDLY
FILL AND DRIFT EASTWARD. OCCLUDED FRONT EXTENDS IN A SHALLOW ARC
ACROSS THE SOUTHERN BERING SEA AND THROUGH THE ALASKA PENINSULA. 25 TO
35 KT EAST TO SOUTHEASTERLY WINDS AND PLENTY OF RAIN ALONG AND IN
ADVANCE OF THE FRONT. THE EASTERN ALEUTIANS AND WESTERN ALASKA
PENINSULA WILL RECEIVE THE BRUNT OF THIS SYSTEM.

FRONT REACHES THE OUTER KUSKOKWIM DELTA AND BRISTOL BAY COASTS
TOMORROW MORNING THEN FALLS APART AS IT ATTEMPTS TO MOVE INLAND
TOMORROW NIGHT. HIGH CLOUDS WILL BEGIN TO MOVE OVER THE SOUTHWEST
MAINLAND LATE THIS EVENING BUT PRECIPITATION SHOULD HOLD OFF UNTIL
TOMORROW MORNING...AND EVEN THEN BE LIMITED TO THE IMMEDIATE COAST.

.LONG TERM FORECAST...

HIGH PRESSURE IN THE UPPER LEVELS HOLDS OVER SOUTHERN MAINLAND ALASKA
THROUGH THE WEEKEND...BUT COLD AIR ALOFT WILL KEEP THE AIRMASS MOSTLY
UNSTABLE. MEANWHILE AT THE SURFACE...A THERMAL TROUGH OF LOW PRESSURE
DEVELOPS ACROSS INTERIOR ALASKA. SUNNY SKIES AND AFTERNOON AND EVENING
SEA BREEZES WILL PREDOMINATE ALONG THE SOUTHERN ALASKA COAST WHILE
SCATTERED AFTERNOON AND EVENING SHOWERS WILL CHARACTERIZE MORE INLAND
AREAS. DAYTIME HIGHS EXPECTED TO EXCEED 70 DEGREES ON SATURDAY AND
SUNDAY IN PORTIONS OF THE KUSKOKWIM VALLEY...SUSITNA VALLEY...AND
COPPER RIVER BASIN.

HIGH PRESSURE ALSO BUILDS OVER THE WESTERN ALEUTIANS...STARTING
SATURDAY NIGHT AND ENCOMPASSING MOST OF WESTERN ALASKA BY LATE SUNDAY
NIGHT. CLOUDY BUT MILD WEATHER EXPECTED FOR THE ALEUTIANS AND BERING
SEA FOR THE WEEKEND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...
MARINE...
FIRE WEATHER...

ASB JUN 11